Catalytic conversion of organic sulfur components of industrial off-gases

ABSTRACT

A process wherein industrial off-gases containing organic sulfur components are contacted with an alumina base catalyst to convert these organic sulfur components to easily removable compounds such as CO2 and S. The catalysts employed comprise an alumina base support in combination with at least one metal selected from strontium, calcium, magnesium, zinc, cadmium, barium and molybdenum employed as promoters. The catalysts have significantly increased service life due to the high resistance to sulfate poisoning.

United States Patent [191 Pearson et al. [4 1 Apr. 3, 1973 s41 CATALYTICCONVERSION OF 2,747,968 5/1956 Pigache ..23/2 5 ORGANIC SULFURCOMPONENTS OF P E E C Th D rimary xammerar omas IN Us OFF GASESAttorney-Paul E. Calrow, Harold L. Jenkins and An- [75] Inventors:Michael J. Pearson, Pleasanton; d E, B l

Orrie C. Olsen, Walnut Creek; James F. Murphy, Danville, all of [57]ABSTRACT Calif A process wherein industrial off-gases containing or-[73] Assignee: Kaiser Aluminum & Chemical Corganic sulfur components arecontacted with an aluporation, Oakland, Calif. mina base catalyst toconvert these organic sulfur components to easily removable compoundssuch as [22] 1971 C0 and S. The catalysts employed comprise an alu- 21App], 117 393 mina base support in combination with at least one metalselected from strontium, calcium, magnesium, zinc, cadmium, barium andmolybdenum employed as /570, promoters. The catalysts have significantlyincreased 423/576 service life due to the high resistance to sulfate[51] Int. Cl. ..B01d 53/34 poisoning. [58] Field of Search...23/2 S, 3L, 178 S, 178, 225 P; 423/230, 244, 245, 570, 571, 576, 564, 567

[56] References Cited 10 Claims, 1 Drawing Figure UNITED STATES PATENTS1,771,481 7/1930 Benner et al ..23/3 L (D ACTIVATED BAUXlTE X SUPPORTSUPPORT Mg m SUPPORT-F00 E SUPPORT Zn 3 i m SUPPORT ca 3|- ACTIVITY 6SUPPORT M0 5 5 5 0 '00 m 8 2 X s E 3% D g g 75' U 5 S: I O 2 o 50- 1 E O5 2 m 51 m c 25- n 0 I 2 a 4 5' s SULFATE as PVATEIITEUAPRB I975 x. Psi5m CATALYTIC CONVERSION OF ORGANIC SULFUR COMPONENTS OF INDUSTRIALOFF-GASES 2 HmOmmDw no .PEQQQDW N FmOamDW 0 .PQOQQDW 2 .FKOQQDW FEOQQDW@XQDBEIQ m m N E V m 3 -3 3. 02 x. t iu MICHAEL J. PEARSON BY ORRIEOLSEN JAMES MURPHY ATTORNEY CATALYTIC CONVERSION OF ORGANIC SULFURCOMPONENTS OF INDUSTRIAL OFF-GASES BACKGROUND OF THE INVENTION Thisinvention provides an improved process for the catalytic conversion oforganic sulfur-containing components present in industrial off-gases.More particularly, it relates to improved alumina base catalystspossessing increased resistance to sulfate poisoning and consequentlyextended service life when employed for the conversion of organic sulfurcontaminants to easily removable compounds.

Many industrial fuels contain sulfur compounds, and prior toutilization, these fuels must be subjected to a desulfurizationtreatment. There are processes which involve the removal ofsulfur-containing compounds from sour crudes, such as sour petroleumcrudes and sour natural gases. The presence of sulfur-containingcompounds renders these crude products unsuitable for most uses due tothe toxic nature of these compounds and the corrosive influence theyexert upon oxidation. Removal of these sulfur-containing components frompetroleum crudes and natural gases is not only important from aneconomic point of view but also from an ecological standpoint. Thesulfuncontaining compounds, particularly those present in sour naturalgases, when released to the atmosphere may cause pollution problems.Thus, elimination of these sulfur-pontaining pollutants by conversion toeasily removable compounds is of major importance and there have beenmany suggestions made to accomplish this result.

In general, sour natural gas contains significant quantities ofinorganic and organic sulfur compounds. To remove thesesulfur-containing contaminants from the natural gas, a so-calledsweetening process is widely applied which consists of absorption ofacidic components, including sulfur-containing compounds in a weaklyalkaline solution such as solutions of ethanolamine, potassium carbonateor, for example, Sulfinol (35 percent diisopropanolamine 40 percentsulfolane 25 percent water, The Oil and Gas Journal, Jan. 22, 1968). Thesweetened or scrubbed natural gas devoid of sulfur compounds can then bedirectly employed for well-known uses without the hazards of sulfurpollution, while the absorbent is regenerated by heating it to drive offthe dissolved sulfur-containing compounds in gas form. The gas removedfrom the absorbent is generally rich in hydrogen sulfide, and it alsocontains significant quantities of mercaptans, polycarbonyl sulfides,together with CO In general, this gas is utilized for the production ofsulfuric acid by intermediate oxidation of the hydrogen sulfidecomponent or for the production of sulfur by partial oxidation. Theoff-gases resulting from the partial oxidation treatment usually containorganic sulfur compounds, commonly in the form of COS and CS and whilethe total quantity of these organic sulfur compounds is only in theneighborhood of l-2 percent, unless they are converted to sulfur and COthey build up to significant quantities and cause pollution of the air.

Conversion of these organic sulfur compounds to elemental sulfur andcarbon dioxide or hydrogen sulfide is generally accomplished byemploying a catalyst capable of catalyzing the decomposition reactionunder oxidative conditions. Commonly activated bauxite or activatedalumina are utilized in the catalytic conversion of these compounds.

0 contain excessive quantities of harmful sulfur com- It has been foundthat during the conversion of these sulfur-containing compounds in theClaus process, there is a gradual build-up of sulfate on the surface ofthe catalyst. This sulfate is believed to be produced by oxidation of S0on the active sites of the bauxite or alumina catalyst employed. Thisresults in accumulation of sulfate on the surface of the catalyst, withconsequent reduction in the activity. Reduced activity causesinefiicient conversion so that the off-gases will pounds, which willescape into the air to cause pollution. Additionally, some of the sulfurproduced by the catalytic conversion can remain on the surface of thecatalyst and during oxidative regeneration needed to remove carbonaccumulated in the catalyst surface, will oxidize to sulfate, furtherdecreasing the activity of the catalyst. Thus, regeneration will not inall instances improve performance and frequently results in theformation of additional sulfate on the active sites. This necessitatesdisposal of the catalyst much sooner than is economically desirable. Inaddition to economic considerations, catalysts of reduced activity usedunder the same conversion conditions as fresh catalysts will be unableto convert the sulfur-containing compounds, resulting in pollution.Thus, it is important from both an economical and an ecologicalstandpoint to provide a catalyst for the conversion of organicsulfur-containing compounds that retains its activity for extendedperiods, even when sulfate deposition occurs.

It has now been discovered that an alumina base support combined withcertain promoters exhibits increased resistance to sulfate poisoning,thus providing significantly longer service life than catalystsheretofore employed.

BRIEF SUMMARY OF THE INVENTION An improved catalyst is provided for theconversion of organic sulfur components of industrial off-gases toeasily removable compounds. The catalysts consist of an alumina basesupport possessing a surface area in excess of about 10 m /g. Thesupport is combined with at least one promoter selected from calcium,strontium, magnesium, zinc, cadmium, barium and molybdenum wherein thepromoter is present in an amount at least about 0.1 percent by weight ofthe catalyst. The catalytic conversion of the organic sulfur componentsis accomplished at temperatures between about and 400 C, preferablybetween about 200 and 400 C, and the improved catalysts provide extendedservice life and high resistance to sulfate poisoning.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE shows a comparison betweenthe relative activities of the improved catalysts and prior artcatalysts employed for the catalystic conversion of organic sulfurcomponents of industrial off-gases, as a function of sulfateaccumulation on their surface.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to thecatalytic conversion of organic sulfur components of industrialoff-gases to easily recoverable compounds. More particularly, itconcerns the utilization of improved alumina base catalysts resistant tosulfate poisoning for the catalytic conversion of organic sulfurcomponents of industrial off-gases.

Under the term of industrial off-gas for the purposes of the presentinvention, by-product gases are understood which contain organic sulfurcomponents.

The expression organic sulfur components refers to organic sulfurcompounds represented by the structures of R-S R-OS, R-Sl-l and R-S-R,where R is carbon or a hydrocarbon. Typical examples of these compoundsinclude carbonyl sulfide (COS), carbon disulfide (CS mercaptans. Theterm catalytic conversion as used herein refers to reactions such as COSH O (vapor) H S +CO 2H S S ZH O 35 2COS S0 2CO 35 wherein conversion ofthe organic sulfur contaminants to CO S and/or H 8 is accomplished bycontact with the improved catalysts of the present invention.

While the well-known Claus process, employed to treat sulfur componentsremoved from sour natural gases, is the main source of off-gasescontaining these organic sulfur components, the improved catalysts ofthe present invention can be successfully employed for anydesulfurization process where the goal is to convert COS and/or CS to COand S or H 8. Thus, for example, the improved catalysts can be used withgood results in the desulfurization of crude petroleum hydrocarbons,provided the desulfurization off-gases contain, for example, COS and/orCS For simplicity and better understanding, the utilization of theimproved catalysts will be described in detail with regard to Clausprocess off-gases without, however, intending to limit the scope of suchutilization to Claus-process off-gases alone.

It has now been surprisingly discovered that alumina base catalysts ofincreased resistance to sulfate poisoning can be made by combining analumina base support with promoters acting as antipoisoning agents whichare selected from metals such as calcium, magnesium, strontium, bariumzinc, cadmium, molybdenum and mixtures thereof. The improved catalystsof the present invention exhibit high activity and consequentlyincreased service life, even with significant accumulation of sulfate ontheir surface, and thus can be utilized for the conversion of organicsulfur components for significantly longer periods than prior artconversion catalysts.

Any of the well-known activated aluminas can be utilized in the presentprocess for the alumina base support, including activated bauxite.Supports which can be successfully utilized are those which haverelatively large surface areas, usually at least 10 and generallybetween about 50-350 m /g, as determined by the wellknown B.E.T. method.Typical supports include, for example, activated bauxite, activatedaluminas possessing an essentially chi-rho structure, calcined Bayerhydrate, calcined gel-derived aluminas containing a substantial portionof pseudoboehmite, gamma alumina and others.

The alumina to be utilized as support for the improved catalysts of thepresent invention can be either in granular or in shaped form prior tocombination with the promoters.

There are several known techniques which allow incorporation ofpromoters into supports, and these techniques can be successfullyemployed in the preparation of the improved catalysts. For example, ithas been found that spherical activated alumina can be combined with thepromoters by impregnation. This involves immersion of the spheres in asolution of the promoter employed in salt form, followed by drying andactivation. It is also possible to include the promoters in the supportby spraying the surface of the support with a solution of the promoters.Further, it is feasible to employ dry. mixtures of the support and thepromoters, co-ground to assure uniform distribution. In any event, nomatter what type of technique is used to combine the promoters with thesupport, it is recommended to employ a medthod which provides preferablyuniform distribution of the promoters on the support.

The suitable promoters or antipoisoning agents capable of rendering thesupport highly resistant to deterioration by sulfate poisoning and whichact as promoters in the catalytic conversion of organic sulfurcomponents include: magnesium, calcium, strontium, barium, zinc, cadmiumand molybdenum. Combinations of these promoters can also be utilized;for example, the support can be simultaneously combined with ions of oneor more metals to obtain the improved catalysts of the presentinvention.

When the combining of the support with the promoter is accomplished bythe impregnation technique, the desired metal cation or cations areincorporated with the support by using an aqueous solution of the salt.Thus, for example, if it is desired to incorporate calcium in thesupport, a water-soluble salt of this metal, such as calcium acetate, isutilized. In general, it was found that the acetate salt of the Group IImetals of Ca, Mg, Cd and Zn, besides being watersoluble, decomposes atrelatively low temperature to the corresponding oxide well within thetemperature range of activation, thus providing a convenient way ofincorporation. Naturally, other water-soluble salts of the above recitedcations can be equally successfully employed. Molybdenum is usuallyapplied in the form of ammonium molybdate.

The amount of promoter to be combined with the support in order toachieve the desired high activity is usually small. It has been foundthat promoter quantities as low as 0.1 percent by weight of thecatalyst, calculated as metal, provided significant increase in theactivity of the catalyst. Particularly good results can be obtained byusing about 1 percent by weight or more promoter based on the weight ofthe catalyst. The upper limit of promoter incorporated into thesubstrate depends on the economy and, in general, it is selected so asto avoid reduction of the surface area below about 10 m /g. Promoterconcentrations between about 1 percent and about 20 percent, andpreferably between 1 and 8 percent, by weight of catalyst were found tobe not only economical, but also highly successful in obtainingcatalysts possessing increased resistance to sulfate poisoning.

Subsequent to incorporation of the promoters in the support, thecatalyst should be dried if impregnation or spraying technique wasemployed. Drying is accomplished in the temperature range within about-12 0 C in any suitable drying equipment. Subsequent to drying, thecatalyst is thermally activated and for the activation, temperaturesfrom about 350 and 700 C were found suitable.

The activated catalysts thus prepared are then suitable to be employedwith excellent results as conversion catalysts for organic sulfurcomponent at temperatures between about 100 and 400 C, and preferablybetween about 200 and 400 C.

The following examples are presented to further illustrate the novelaspects of the present invention and to provide a comparison between theactivities of the improved catalysts and also of those employed by theprior art.

EXAMPLE I Spherical active alumina, characterized by the followingproperties, was impregnated with various Group II metal salts to providethe improved conversion catalysts.

TABLE I Characterization of the Alumina Suppo A1 0 content 93.6 LOl(Loss on Ignition) 70 6.0 Surface area m /g 302 Major phase chi-rhoBatches of spherical alumina were immersed in aqueous solutions ofcalcium acetate, magnesium acetate, cadmium acetate and zinc acetate,for a period of about 2 hours. Each batch was then dried at about 104 Cfor 2 hours, followed by activation at about 450 C for 1 hour. Theloading of the spheres with the promoters was then measured, and theresults are shown in Table II.

TABLE ll Loading of Support with Promoters Concentration of PromoterImpregnating soln. Promoter (as metal) Type by wt. by wt. of catalystCa-acetate 26 3.52 Ca Mg-acetate 30 3.84 Mg Cd-acetate 17 6.40 CdZn-acetate 2.59 Zn TABLE III S0 Content in System by Wt. of CatalystAl,O -Ca 7.70 Al,O -Mg 5.96 Al,O -Cd 5.00 Al,0,-Zn 4.37 UnimpregnatedSupport 6.90 Unimpregnated Bauxite 12.80

The conditions established above correspond to a catalyst use of about2,0004,000 hours under usual plant conditions and are intended toreproduce the sulfate accumulation expected on the surface of theconversion catalysts after being employed in the Claus process.

Each catalyst batch, including the controls, was then tested foractivity in a manner described below. 35 grams of each catalyst and alsoof the controls were placed in individual reactors (bed thickness 2.4 Xl 1.0 cm) maintained at about 275 C. A gas composition containing COS4%, S0 2%, H 0 8%, balance nitrogen (all percentages are volumepercent), was conducted through each reactor at a flow rate of 300 em/minute and the activity was measured and recorded, the results beingshown in Table IV below. (Activity percent is calculated on the basis ofvolume COS converted.)

TABLE IV Original activity Activity of SO" in conversion of containingcatalyst Catalyst System COS (no S0,, on in conversion 4 surface) of COSAl o -Ca 100 84.0 Al o -Mg 100 72.0 A1 0 -Cd 100 96.0 Al,O -Zn 100 92.0Support-control l00 34.0 Bauxite-control 100 0 The activities of theimproved catalysts and that of the controls were plotted as a functionof sulfate accumulation on the surface and are shown in the FIGURE. Itcan be observed that the activity of bauxite decreases rapidly withaccumulation of sulfate on the surface and reaches zero activity atabout 5 percent sulfate content on the surface. The unimpregnatedactivated alumina of essentially chi-rho structure, while markedlybetter than the activated bauxite, will exhibit about 34 percentactivity, i.e., 34 percent of the original activity, when the sulfatecontent on its surface reaches about 6 percent. In contrast, all of theimproved catalysts having about 5-6 percent sulfate on their surface,still exhibit an activity of at least percent of their originalactivity, thus providing a catalyst of significantly improved activityand service life. The tests were also repeated with a gas mixturecontaining CS and the results obtained corresponded substantially tothose obtained with COS as far as the conversion activities wereconcerned.

EXAMPLE II The tests described in Example I were repeated by usinggranular activated bauxite as support. Batches of catalysts wereprepared employing the same promoters used in Example I, and the batcheswere subjected to the sulfate accumulation procedure to obtain a sulfateconcentration of about 5 percent on the surface of the control and onthe surface of the impregnated catalysts. Following the sulfateaccumulation procedure, the catalysts and the control were subjected tothe COS conversion test described in Example I, and it has been foundthat while the control exhibited 0 percent activity, the impregnatedcatalyst samples, particularly the Ca, Cd, and Zn treated samples, stillexhibited economically significant activity, establishing thatincorporation of the promoters recited hereinabove increasesignificantly the resistance of the catalysts against sulfate poisoning.

EXAMPLE III Compositions containing Group VI and Group VIII metals werealso tested to establish their resistance to sulfate poisoning. Thus,individual batches of spherical alumina of the type shown in Table I,were impregnated with solutions of the salts of iron, cobalt, nickel(Group 1 VIII), and chromium (Group VI). The compositions, together witha batch of unimpregnated activated alumina, were then treated with SO-air in accordance with the procedure described in Example I and theiractivity was determined. The results are shown in Table V below. Inaddition, a batch of activated alumina was impregnated with an ammoniummolybdate solution (Group VI). This batch was also subjected to thetests described in Example I. The results of these comparison testsindicate the selectivity that exists for certain metals when in anenvironment where sulfate poisoning occurs.

TABLE V Concentration of Metal in Sulfate Activity in Metal Catalyst onsurface COS conversion Iron 5.35 19.7 Cobalt 3.86 9.64 l6 Nickel 3.8319.1 0 Chromium 2.83 16.9 0 Molybdenum 8.0 4.2 90

What is claimed is: 1. A process for the catalytic conversion of organicsulfur components of industrial off-gases resulting from the Clausprocess to carbon dioxide, easily removable inorganic sulfur compoundsand elemental sulfur which comprises contacting the off-gases at atemperature between about and 400 C with a catalyst comprising analumina base support possessing a surface area at least about 10 mlg anda promoter combined with the support in an amount at least about 1.0percent by weight of the catalyst, the promoter being selected from atleast one metal of the group consisting 0 of calcium, strontium, barium,magnesium, cadmium,

6. The process of claim 1, wherein the promoter is zinc.

7. The process of claim 1, wherein the promoter is cadmium.

8. The process of claim 1, wherein the promoter is calcium.

9. The process of claim 1, wherein the promoter is magnesium.

10. The process of claim 1, wherein the promoter is molybdenum.

2. The process of claim 1, wherein the promoter quantity in the catalystis from about 1 percent to about 20 percent by weight of the catalyst.3. The process of claim 1, wherein the contacting is accomplished at atemperature between 200* and 400* C and the surface area of the supportis greater than about 50 m2/g.
 4. The process of claim 1, wherein thesupport is a spherical alumina possessing essentially a chi-rhostructure.
 5. The process of claim 1, wherein the support is anactivated bauxite.
 6. The process of claim 1, wherein the promoter iszinc.
 7. The process of claim 1, wherein the promoter is cadmium.
 8. Theprocess of claim 1, wherein the promoter is calcium.
 9. The process ofclaim 1, wherein the promoter is magnesium.
 10. The process of claim 1,wherein the promoter is molybdenum.